1. Field of the Invention
This invention relates to data I/O transaction method capable of transacting the mixture of one page I/O requests and a multiple-page I/O request, and, more particularly, to a data I/O transaction method and system including a multiple-pages I/O method which is suitably used when a high speed response to one page I/O request is needed.
2. Description of the Prior Art
For example, a computer system for transacting bank deposit works needs to be provided with a region for storage programs or data. In general, a high speed semiconductor memory is used to serve as the main storage device. However, with increment of the programs and data, a method has been widely used in which a cheap direct access storage device (abbreviated to "DASD" hereinafter) such as a magnetic disk is also used as a compliment to an expensive semiconductor memory serving as the main storage device so that the storing system thereof is made hierarchic such that programs or data is input from the DASD to the main storage device at needs. However, such computer system suffers from a problem that the DASD has a poor transacting speed with respect to a central processing unit (abbreviated to "CPU" hereinafter) and the overhead of its CPU used for I/O transaction cannot be negligible. In order to overcome the above-described problems, a multiple pages I/O transaction was invented. The multiple pages I/O transaction is a transaction capable of reducing the overhead of the CPU thereof by I/O transacting multiple pages corresponding to one I/O request as an alternative to the transaction in which I/O transaction is performed by one page unit. It is the transaction capable of shortening the seeking time or searching time over the DASD on which multiple pages of data to be input/output are physically adjacent, wherein the word "page" represents the minimum unit, the word "one page I/O" represents an I/O of one page, and the word "multiple pages I/O" represents an I/O exceeding one page. This multiple pages I/O transaction leads to a fact that the throughput of such CPUs can be improved.
In general, the time required for transacting multiple pages is in proportion to the number of pages transacted by one multiple pages I/O transaction. Therefore, the transacting time takes a longer time in accordance with increment of pages to be transacted in one transaction. In the above-type of conventional technology, such number of pages is fixed as predetermined regardless of the quantity of the I/O request.
However, in the above-described type of bank deposit operation, the number of requests generated for a unit time period in an ON-LINE transaction (one page I/O) usually tends to be changed in accordance with the period of time in a day. If an ON-LINE I/O request (one page I/O request) to the DASD is generated after a massive (the number of pages is great) multiple pages I/O transaction has been started in the same specific DASD, execution of transacting this one page I/O request needs to be waited until the time at which the preceding one multiple-page transaction is completed (two I/O transactions cannot be performed simultaneously). Therefore, a problem arises that the response to the ON-LINE I/O request becomes excessively poor. Such time delay generated in execution of transacting the ON-LINE I/O request becomes larger in the period of time in which the number of ON-LINE I/O requests for a unit time period are great, and the more the number of pages to be in one multiple pages I/O transacted. The number of I/O requests (frequency) generated in one system for a unit time period changes greatly between the busy time period and the slack time period. For example, a system to which requests are generated at an average of 10 to 20 clock periods in the busy time period in the daytime is changed in its period to a second unit in the nighttime.
However, in the above-described type of the conventional technology, the unit when the multiple pages I/O transaction is performed as described above is fixed. Therefore, any regard is not paid for determining this unit so as to make this unit correspond to the change in the number of one page I/O requests for a unit time period in accordance with the period of time in a day.